I don't see how thy contrast each other. The title indicates with the "put" in imperative that you should smile despite what's happening and that is what the uke does. He has to pretend everything is fine on the outside because of the blackmailing stuff forcing him to do things he doesn't want to do.
Welp this is how I see it. The phrase is usually "Put a smile on (someone's face)" which would mean to make someone happy, it contradicts from what the seme is doing rn. As I've said idk how its gonna progress, my guess is that the uke is gonna be the person who "puts a smile (a genuine one) on the seme's face. It's different from "Put on a smile", which can be read like what you have mentioned, that you gotta "put on a smile even though shit happens".
oh, that's a good point
That moment when the title and content contrasts each other :"
Idk about upcoming chapters tho, hopefully seme will get a taste of his own medicine before having a development （/TДT)/